This nonprovisional application claims priority under 35 U.S.C. xc2xa7119(a) on Patent Application No(s). 2002-071243 filed in JAPAN on Mar. 15, 2002, which is (are) herein incorporated by reference.
1. Field of the Invention
This invention relates to an apparatus for reducing noise in an image signal.
2. Description of the Related Art
When a CCD has a large number of pixels, the area per pixel is small. Since the amount of signal obtained from a single pixel is small, the amount of noise is great. There are instances where filtering is applied to an image signal in order to reduce noise. If filtering is applied to image signals indiscriminately, however, image quality declines. Further, edge enhancement often is performed in order to raise the apparent image quality of an image. However, edge emphasis processing enhances noise as well.
An object of the present invention is to make image noise less noticeable.
According to the present invention, the foregoing object is attained by providing a noise reducing apparatus comprising a first noise reducing circuit (means), to which a noise-reduction-target image signal (inclusive of not only an analog signal but also digital image data) representing an image to undergo noise reduction is input, for reducing a noise component and outputting a resultant first image signal; an edge extracting circuit (means) for extracting an edge signal from the first image signal output from the first noise reducing circuit; and an adding circuit (means) for adding the edge signal, which has been extracted by the edge extracting circuit, and the noise-reduction-target image signal and outputting the result.
A control method suited to the above-described noise reducing apparatus according to the present invention also is provided. Specifically, the method comprises the steps of inputting a noise-reduction-target image signal, which represents an image to undergo noise reduction, to a noise reducing circuit (means); obtaining a first image signal in which a noise component has been reduced; extracting an edge signal from the first image signal output from the noise reducing circuit; and adding the edge signal extracted and the noise-reduction-target image signal.
In accordance with the present invention, the noise component is reduced in a noise-reduction-target image signal, which represents an image to which noise reduction is to be applied, whereby a first image signal is obtained. An edge signal representing the edge of the image is extracted from the first image signal obtained. The edge signal extracted and the noise-reduction-target image signal are added.
Since the edge signal is extracted from the first image signal, which has already undergone noise reduction, the noise component will already have been reduced. Accordingly, even though edge enhancement processing is executed by adding the edge signal to the noise-reduction-target image signal, it is possible to prevent noise from being enhanced by edge emphasis. Noise can be reduced while improving apparent image quality by edge emphasis.
The apparatus may further comprise a second noise reducing circuit (means), to which the noise-reduction-target image signal is input, for reducing a noise component and outputting a resultant second image signal (the first noise reducing circuit and the second noise reducing circuit may be the same circuit). In this case, the adding circuit would add the edge signal, which has been extracted by the edge extracting circuit, and the second image signal and output the result.
Since the noise component of the noise-reduction-target image signal per se is reduced, image noise becomes less noticeable. Moreover, since edge emphasis processing is executed by adding the edge signal to the second image signal in which noise has been reduced, the apparent image quality is improved by edge emphasis and it is possible to prevent a decline in the quality of an image represented by the signal output from the adding circuit.
The first noise reducing circuit or the second noise reducing circuit may be so adapted that the extent to which the noise component is reduced can be adjusted.
It is also possible to so arrange it that an edge signal is extracted from the noise-reduction-target image signal and processing is executed for reducing the noise component of the edge signal extracted. The edge signal in which the noise component has been reduced and the noise-reduction-target image signal are added.
Other features and advantages of the present invention will be apparent from the following description taken in conjunction with the accompanying drawings, in which like reference characters designate the same or similar parts throughout the figures thereof.